Methods :
Thirty-two vitreoretinal membrane specimens were collected by sequential peeling during vitrectomy from 32 eyes of 31 consecutive patients. Excised tissues were formalin fixed and whole mounted on glass slides for optical microscopy. Images of unstained samples were obtained under transmitted light, phase contrast and polarized light to evaluate tissue morphology, birefringence (yes/no), pigmentation (yes/no) and pigment distribution (diffused/clustered). Imaging after staining with haematoxylin was performed for the semiquantification of the amount of cell nuclei (low, intermediate, high) and the evaluation of their distribution (homogeneous/clustered) within the sample. In selected samples, immunohistochemical staining for α-smooth muscle actin (anti-α-SMA) was performed. Data were analyzed after grouping according to the following tissue types: ILM only (n=10), ERM only (n=6), ILM+ERM (n=10), proliferative vitreoretinopathy (PVR) (n=6).

Results :
ERM and PVR specimens presented higher cellularity than ILMs. Specimens containing both ERM and ILM showed intermediate cellularity between ILM and ERM group. Birefringence was present in all ERM specimens, but only in 5/10 (50%) of ILMs. High amount of pigment was found only in PVR specimens, but intermediate amount of pigment was occasionally present also in 2/6 (33%) and 1/10 (10%) of ERM and ILM specimens, respectively. Pigmentation was compartmentalized inside the cell-like structures or diffused in the extra-cellular matrix. Leucocyte-rich vessels were present in a PVR specimen from a diabetic patient (Fig. 1). Positivity to anti-α-SMA was found (Fig. 2).

Conclusions :
The microscopic characterization of the surgically removed vitreoretinal membranes can provide information on characteristics of the tissues involved in the retinal diseases, confirming the presence of cellular components involved in the pathogenesis and progression of vitreoretinal diseases.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.